In the manufacture of heat exchangers such as automotive radiators and air conditioner evaporators many elements are assembled to form a core and are held together by steel bands for subsequent processing. The banded cores are subject to wash, flux, and brazing processes. It is critical that the band strap does not loosen from the core after it has been banded, especially in the brazing process, where the core is subjected to temperatures in excess of 1000.degree. F. Failure in any of these stages would result in damage to the core and could also cause damage to the processing equipment. It is also essential that the strap itself or the application of the strap does not damage the core.
Apparatus for applying straps to such cores, known as band heads, typically employ a four step process for banding: feed, tension, crimp, and cut. In the feed cycle, strap is fed from stock material through a track which encloses the core. When the feeding is complete, the end of the strap is clamped and the tensioning step begins. The tensioning comprises pulling the strap from the opposite direction from which it was fed, thereby pulling the strap out of the track and around the core such that the strap overlaps its end. When the desired tension is reached, the strap is fastened or crimped at the overlap region to create a seal around the core. Then the strap is cut to separate the sealed loop portion of the strap from the stock material.
A number of techniques are known for securing the ends of the straps together. One band head requires an external clip to hold the strap ends, thereby mandating that a supply of the clips be maintained. Another known band head uses a key-hole notching approach which produces a strong seal but has short tool life.